1. Field of the Invention
The present invention relates to a method and apparatus for inspecting a photosensitive material for surface defects and, more particularly, to a method and apparatus for inspecting a thermal-developable photosensitive material for defective surface portions by using a reflex-type optical sensor.
2. Description of the Related Art
In recent years, in the field of production of films for medical diagnosis and photoengraving films, there has been a strong demand for reductions in the amounts of waste processing solutions from the viewpoint of environmental protection and space saving. Therefore, techniques are required which relate to a thermal-developable photosensitive material formed as a film for medical diagnosis and a photoengraving film and capable of efficient exposure with a laser image setter or a laser imager and forming a black image having a high resolution and a high degree of sharpness. The thermal-developable photosensitive material has the advantages of requiring no processing chemical solution and enabling clients to be supplied with a thermal-development processing system which is simpler and is designed to avoid any damage to an environment.
The thermal-developable photosensitive material is made by applying materials for a photosensitive layer, a protective layer, etc., to a flexible substrate (hereinafter referred to as a web). In the thermal-developable photosensitive material made in this manner, there is a possibility of a break, a contamination, a pinhole, a streak defect or the like existing in the surface on the photosensitive layer side. Therefore, it is necessary to detect such defective surface portions of the thermal-developable photosensitive material.
As a method of optically inspecting a photosensitive material for defective surface portions, a reflection-type method is known in which a photosensitive material is inspected by irradiating the surface of the photosensitive layer with inspection light from a laser oscillator and by using light reflected by the surface of the photosensitive layer. Another method known as a method of optically inspecting a photosensitive material is a transmission-type method in which a photosensitive material is inspected by monitoring light transmitted through the photosensitive layer. It is advantageous to use the transmission-type method rather than the reflection-type method for detection of a pinhole or a coating discontinuity in a photosensitive layer, which is a fatal defect.
The above-described thermal-developable photosensitive material used without a step for dissolution in a solution unlike conventional photosensitive materials which undergo solution-development has a high degree of transparency and only a small difference in density at a defective portion in its surface. Therefore, it is difficult to detect defective surface portions of the thermal-developable photosensitive material by using a transmission-type optical sensor.
Japanese Patent Application Publication No. 53-118089 discloses a method of detecting defective surface portions with a reflex-type sensor. That is, a defective surface portion of the thermal-developable photosensitive material has a diffuse reflectance higher than that of the normal portion and the quantity of specular reflected light from the defective portion is smaller than the quantity of the specular reflected light from the normal portion. As shown in FIG. 6(A), when the normal portion is irradiated with inspection light, a large amount of the specular reflected light 2 is received by a light-receiving portion 1. In contrast, when the defective surface portion is irradiated with inspection light, the quantity of the specular reflected light 2 is reduced, as shown in FIG. 6(B). It is possible to detect the defective surface portion in accordance with this reduction in quantity of light from the normal value.
However, there is a problem that the reflex-type optical sensor is incapable of detecting a defective portion with accuracy when the change in diffuse reflectance across the defective surface portion is small. That is, when the change in diffuse reflectance across a defective surface portion is small, the change in the quantity of the specular reflected light 2 is also small. Under this condition, the resulting change in the quantity of light received by the light-receiving portion 1 is extremely small since part of diffuse reflected light 3 is received by the light-receiving portion 1. For this reason, defective surface portions across which only a small change in diffuse reflectance is recognized cannot be detected with accuracy by using the reflex-type optical sensor. The light-receiving area of the light-receiving portion 1 may be reduced to avoid receiving of diffuse reflected light 3. The sensitivity is thereby improved to some degree. However, if the light-receiving area is reduced, the adaptability of the optical sensor to inspection of other objects which may be selected is reduced. This problem is encountered not only in the case of detection of defects in the thermal-developable photosensitive material but also in the case where defect portions in a transparent photosensitive material are detected with a reflex-type optical sensor.
In view of the above-described circumstances the present invention is achieved and, an object of the present invention is to provide a surface defect inspection method and apparatus capable of inspecting a photosensitive material for defective surface portions with efficiency by using a reflex-type optical sensor.
To attain the above-described object, the present invention is directed to a surface defect inspection method of inspecting a photosensitive material for defective surface portions by using a reflex-type optical sensor, comprising the steps of: irradiating the photosensitive material with inspection light from a light-emitting portion of the reflex-type optical sensor; receiving, through a light-receiving portion of the reflex-type optical sensor, light in a reflected part of the inspection light reflected by the photosensitive material while cutting out specular reflected light in the reflected part of the inspection light; and checking a defective surface portion in the photosensitive material in accordance with a change in a quantity of the light received through the light-receiving portion.
The present invention is also directed to a surface defect inspection apparatus which inspects a photosensitive material for defective surface portions by using a reflex-type optical sensor, wherein the reflex-type optical sensor comprises: a light-emitting portion which irradiates the photosensitive material with inspection light; a light-receiving portion which receives light in a reflected part of the inspection light reflected by the photosensitive material; and a shielding member which cuts out specular reflected light in the reflected part of the inspection light traveling to the light-receiving portion.
According to the present invention, specular reflected light in the reflected part of inspection light reflected by the photosensitive material is cut out and only diffuse reflected light in the reflected part of the inspection light is received, thereby increasing changes in the quantity of received light due to defective surface portions and enabling the defective surface portions to be checked with accuracy.
Preferably, a transmission-type optical sensor is used as well as the reflex-type optical sensor to enable a pinhole, a coating discontinuity or the like, which are detected more preferably by the transmission type, to be checked with efficiency.
Preferably, a selection can be made from a state where the specular reflected light is cut out and a state where the specular reflected light is not cut out, thereby enabling other photosensitive materials requiring receiving specular reflected light to be inspected for defective surface portions with efficiency.